Reconstructing atmospheric nitrogen pressure from N2-Ne-Ar systematics in quartz-hosted fluid inclusions

Atmospheric nitrogen (N₂) is the dominant constituent of Earth’s atmosphere and exerts a first-order control on surface pressure, climate sensitivity(1), and long-term habitability(2). Despite its importance, quantitative constraints on past atmospheric nitrogen partial pressure (pN₂) remain limited(3). Fluid inclusions in hydrothermal quartz record the composition of crustal fluids as well as the composition of Earth’s ancient atmosphere (4, 5), but reconstructing atmospheric pN₂ from inclusions is complicated by radiogenic overprints and fluid evolution(6). We present a new method using N₂-Ne-Ar elemental and isotopic systematics applied to fluid inclusions in ~20 Ma quartz veins from the Alps and Himalaya mountains ranges in order to evaluate the preservation of atmospheric nitrogen signals. Mixing relationships between N₂/²²Ne and ²¹Ne/²²Ne are used to distinguish atmospheric components from crustal contributions, with nucleogenic ²¹Ne tracing crustal inputs. Linear trends allow extrapolation to air-saturated water endmembers and reconstruction of atmospheric pN₂. Samples from low-grade geological contexts yield pN₂ estimates consistent with the modern atmosphere, indicating closed-system behavior after entrapment. In contrast, samples influenced by syn-tectonic metamorphism show excesses in N₂ (elevated apparent pN₂), reflecting addition of crustal nitrogen. These results demonstrate the potential of combining fluid inclusions and noble gas geochemistry to link crustal fluid processes with atmospheric evolution.

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This work received funding from the European Research Council (ERC) under the European Union's Horizon Europe Research and Innovation Program (Grant Agreement 101041122 to Guillaume Avice).